Improve uploadssc command verbiage

[hakusaro]

The current uploadssc command verbiage is unclear as to what data it will upload, and if you can run the command back to back successively and what exactly that will do. It should provide guidance on which data (when the user joined most recently but at the moment they connect, not historically the first connection) is uploaded. It should also describe what will happen if run back to back to back on a user after being run the first time or if they already have SSC data.

This is inspired by #1738.